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Realistic electron beam spectra: Measurements and dosimetric effects
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R EA LISTIC E LECT R ON B EAM SP ECTRA : MEASUREM EN T S AN D DO SIMETRIC EFFECT S J.O. Deasy, P.R. Almo nd , Brown Canc er Center, University of Louisville, and M.T. Mc Elli st re m , Dep t . of Physics and Astronomy , University of Kentucky, USA . Elect ron energy spectra and angular d ist rib ut ion s were measured usin g magnetic spectrometer t ech niques , at isocen t er , for t wo clinical lin ea r acc ele rators: on e scan ning beam (T herat ronics T 20) an d one scattering-foil (P hilips 5L 25) m ach ine . T he ene rgy spectra of t he T 20 wer e all of nearly Gaussia n sha pe an d en ergy full-wid th at- hal f-maxim um -intensity (FWHM) of about 5%. The energy distributions of the SL25 were of va ried and unus uaJ shapes, includ in g shap es even with do uble peaks, a nd had energy F WHM from 9-22% . P eak spec t ral shapes for t he 5L25, in some cases, were ob ser ved t o change over ti me . T he effect of these varied spect ra on depth -dose curves can be charac t erize d by th e spectral quanti ty < Eo > ", which is defined her e as t he mean energy of th e incide nt spectral peak, termed t he "peak-m ean-energy" . An analy tical model shows that, in the ab se nce of elect rons at the patien t p lane with energies outside abo ut < Eo > " ±0.1 < Eo >", R; and Rso are both determined by < Eo > ". T his is confirmed by a Mon te Ca rlo calculation com pa ri ng dep th -dose curves from two di fferent idealized incident spectra . In addition, Monte Carlo depth-do se sim ulat ions based on the measu red linac en er gy spectra show that t he energy spread has on ly a small effect on t he shape of the cen t ral axis dep t h- do se curve, eve n for FWHM as large as 20% . Furthermore , t here is a mu ch better correlation between the MC-derived Rp's a nd t he pea k-m ea n-energies « Eo > "' s) th an between the Rp's and t he most pr o bable en ergi es (Ep,o's ). T hese resu lts imply that t he peak-m ean-energy is a more ap prop riate spectral quantity t o use when des cribing elec tron beam s at t he surfac e com pared to t he mos t probable ene rgy , Ep,o.
nRAM QUALITY SPECIPICATION FOR ACCURATIi DOSiMB'rRY
119 MONTE-CARLO SIMULATION OF THERAPY ACCELERATORS APPLICATION TO A MMSO RACETRACK MlCROTRON
OFBLECrRON AND PHaroNBBAMS
AndeR Brahme
D~t of Modical RadIation Phyalcs, Karollnska lnltitulel ond Stockholm UnlVllllllty, P.O. BOl{ 260, S-171 76StOl;lholm, Sweden
Beam qulllity speclflcatlon for aceurata do&imctry of cllniclll eleetron and photon beams Is compllcllted by the large variation In thedesign of the beam dlaplngl)'81etPl wllh regard to /iIctonlie the Inlrloslo aoc:eIeralor
beam and beam natteniol. nlOlIltorilll and colllmlllion systoma. For electrons tbe beam Ihaplnglyltem may seneratea broadet energy dlltrlbuticm of the initial eleolroll boatit and generate seconcllrY and scattund c:IeotroDl in coIUmalon In addition to the somelImesllll'p photon eontaminatiOll. AU of thee faoWtJ liave 10 be taken into llOCOIlllt lor accurm dos1melry of &IedrOD beam, butto a VBl)'ing degree at different dep\hIin the patienL The lIeCloodary IIDd obliquely IC8ttcred electrons give ftII Increued surlau dOI8 wbmaa die photon contamination lllCl'elSCll the dolo bet_ the IIIrr_ anddolo 1lWl1mum of the oIectrOII beam, Sinoe theeo COmponSllts bave dIfferent slopping power ratiOl (sw,a) or mom .:ouratoly dIfferent Olw,a 'Ill1UBI (lDl1,. '" sW,a • W/e) ascom(lllted to the pure pdlUary olcotron beam, accurate doslnietry of Iheae bellll1l will be qulle complex. POI photon beams !be situation il simpler eY1lll though the dl'8lgn of the lIIl'get I\IId flalllllling system bu a conaidorable lnt1uence on theboam quality, On Dne extreme end II SOI11ll new 20 MV IIlIICblnea with beam hnrdtztIng f1allell!ng filters of low atomlo nombet IIllIkIns vetj' penetrative narrow beamsnear theCBllll'al axil whereu the periphery of brol!d beams Ismuch 10fler. A maah more VDlfonn brow! beam pfOfilllat rI1 depths II obllllned willi lIOIIloed photon blllllUJ whllll> the bardeat pboton oompooent 18 at theperiphery of thebeam to oompemalci tor the ionget raylengtb. In betwlloo IlI'O spectrally compensating lillOl'll and the mosl common group using thick high atomic IIUmbor flitlit'. Doe to tIICl ciCIO relatloo between Jlen ond I\> it can be sbown lhat aIlonuatiDll dala am 'I8Il cloacly related to the ef'feotive llOppinl power ratio of photon beams, However, some authon have proposed the useof beam modifiers snc:h as clcc:troll film or special nmow blllll1 ool1lmlton for detennInatlon of beam attenuation . This should be avoided as far. possible as the beam to be IllCIIIQred will beoonsIdenbly Inf1uooc:ed bytbem and!hilithedosimetry more unc:ertaIn.
120 ON AXIS AND OFF AXIS BREMSSTRAHLUNG ENERGY SPECTRA CALCULATED BY EGS4 MONTE~ARLO CODE
SHI LIU. PEDROANDREO,ANDERS SATIlERBERGI,IRENA GUDOWSKA and ANDERSBRAHME Dept Medical Radiation Physics, Karolinska Institutet - University of Stockholm, S-I71 76 Stockholm, Sweden; I Dept Radiation Physics, University of Umea, S-901 85 Umea, Sweden
S. ZEFKILI, InstitutPaoli·GaJmeltes, Marseille, FRANCE G. MALA-TARA, K. KAPPAS, Universityof Palras, Patras, GREECE J .C . ROSENWALD,lnstftut Curie, Paris, FRANCE
Within the frame of our programme on realistic Monte Carlo calculations for dosimetry and treatment planning, the detailed simulation of the treatment head of radiotherapy accelerators has been focused on a MM50 Racetrack microtron . The project includes the improvement of bremsstrahlung target design and the effect of neutron production on the irradiation of patients with high-energy scanned beams. Most applications by other autho rs have so far used the EGS4 Monte Carlo system.; their implementation has been usually based on the coding of the speci fic geometry of each machine. Our project concentrates in using " public" and standard ized software tools for both geometry descr iption and simulation to minim ize manpowe r and economi cal requ irem ents. Accelerator head structures are described using the Combinatorial Geometry (CG) package where 3D "bodies" are combined using Boolean algebra; this enables an almost universal characterization that can be easily adapted to any accelerator treatment head. Graphical visualizatio n is accomplished with the code SABRINA, which processes both CG (and specific input s for the MCNP Monte Carlo system); SABRINA runs in almost every UNIX workstation. Simulations are performed with the ACCEPT code of the ITS 3.0 MC system , full y based on CG inputs and containing "state- of-the-art" brems strahlung cross·sections; it also allows a direct implementation of the purging magnet in the MMSO head. Our interest in neutron production will consider the utiliz ation of MCNP when a planned version containing the electron transport of ITS 3.0 becomes a reality. All the software is available in Europe through the NEA data bank . This presentation will describe the selected tools and actual status of the project. Support from K Van Riper (LANL) and R Kensek and J Halbleib (Sandia Labs) is greatly acknowledged.
For accurate 3D treatment planning new models of dose calculation are being developed which require the knowledge of the energy spectra of photons incident on the surface of the patients. In this study the EGS4 Monte·Carlo code system wrth the PRESTA electron transport algorithm was used in order to compute the photon energy spectra at on axis and off-axis points for a number of Iinacs manufactured by G.E. The different parts 01 the accelerator head were modeled by simple geometrical volumes and the photon beams were produced by simulating the bombarding of the target wrth monoenergetic electron beams assumed to have a spatial distribution. The analysis of the cak:IJlated spectra wrth and without flattening filter showed us the photon beam quality variation at off-axispoints. To verify the validity of the calculated spectra we introduced them as input to a dose spread arrays convolution program in order to calculate TMRas a functionof depth of the total and primary dose distribution in a water1ike fantom. The calculated depth dose distributions were compared with experimental data . The theoretica l and experimental resuns are consistent and allow us to consider that the photon energy spectra can be determined with acceptable accuracy using Monte Carlosimulations even with a simptrtied acce lerator head geometry.
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R EA LISTIC E LECT R ON B EAM SP ECTRA : MEASUREM EN T S AN D DO SIMETRIC EFFECT S J.O. Deasy, P.R. Almo nd , Brown Canc er Center, University of Louisville, and M.T. Mc Elli st re m , Dep t . of Physics and Astronomy , University of Kentucky, USA . Elect ron energy spectra and angular d ist rib ut ion s were measured usin g magnetic spectrometer t ech niques , at isocen t er , for t wo clinical lin ea r acc ele rators: on e scan ning beam (T herat ronics T 20) an d one scattering-foil (P hilips 5L 25) m ach ine . T he ene rgy spectra of t he T 20 wer e all of nearly Gaussia n sha pe an d en ergy full-wid th at- hal f-maxim um -intensity (FWHM) of about 5%. The energy distributions of the SL25 were of va ried and unus uaJ shapes, includ in g shap es even with do uble peaks, a nd had energy F WHM from 9-22% . P eak spec t ral shapes for t he 5L25, in some cases, were ob ser ved t o change over ti me . T he effect of these varied spect ra on depth -dose curves can be charac t erize d by th e spectral quanti ty < Eo > ", which is defined her e as t he mean energy of th e incide nt spectral peak, termed t he "peak-m ean-energy" . An analy tical model shows that, in the ab se nce of elect rons at the patien t p lane with energies outside abo ut < Eo > " ±0.1 < Eo >", R; and Rso are both determined by < Eo > ". T his is confirmed by a Mon te Ca rlo calculation com pa ri ng dep th -dose curves from two di fferent idealized incident spectra . In addition, Monte Carlo depth-do se sim ulat ions based on the measu red linac en er gy spectra show that t he energy spread has on ly a small effect on t he shape of the cen t ral axis dep t h- do se curve, eve n for FWHM as large as 20% . Furthermore , t here is a mu ch better correlation between the MC-derived Rp's a nd t he pea k-m ea n-energies « Eo > "' s) th an between the Rp's and t he most pr o bable en ergi es (Ep,o's ). T hese resu lts imply that t he peak-m ean-energy is a more ap prop riate spectral quantity t o use when des cribing elec tron beam s at t he surfac e com pared to t he mos t probable ene rgy , Ep,o.
nRAM QUALITY SPECIPICATION FOR ACCURATIi DOSiMB'rRY
119 MONTE-CARLO SIMULATION OF THERAPY ACCELERATORS APPLICATION TO A MMSO RACETRACK MlCROTRON
OFBLECrRON AND PHaroNBBAMS
AndeR Brahme
D~t of Modical RadIation Phyalcs, Karollnska lnltitulel ond Stockholm UnlVllllllty, P.O. BOl{ 260, S-171 76StOl;lholm, Sweden
Beam qulllity speclflcatlon for aceurata do&imctry of cllniclll eleetron and photon beams Is compllcllted by the large variation In thedesign of the beam dlaplngl)'81etPl wllh regard to /iIctonlie the Inlrloslo aoc:eIeralor
beam and beam natteniol. nlOlIltorilll and colllmlllion systoma. For electrons tbe beam Ihaplnglyltem may seneratea broadet energy dlltrlbuticm of the initial eleolroll boatit and generate seconcllrY and scattund c:IeotroDl in coIUmalon In addition to the somelImesllll'p photon eontaminatiOll. AU of thee faoWtJ liave 10 be taken into llOCOIlllt lor accurm dos1melry of &IedrOD beam, butto a VBl)'ing degree at different dep\hIin the patienL The lIeCloodary IIDd obliquely IC8ttcred electrons give ftII Increued surlau dOI8 wbmaa die photon contamination lllCl'elSCll the dolo bet_ the IIIrr_ anddolo 1lWl1mum of the oIectrOII beam, Sinoe theeo COmponSllts bave dIfferent slopping power ratiOl (sw,a) or mom .:ouratoly dIfferent Olw,a 'Ill1UBI (lDl1,. '" sW,a • W/e) ascom(lllted to the pure pdlUary olcotron beam, accurate doslnietry of Iheae bellll1l will be qulle complex. POI photon beams !be situation il simpler eY1lll though the dl'8lgn of the lIIl'get I\IId flalllllling system bu a conaidorable lnt1uence on theboam quality, On Dne extreme end II SOI11ll new 20 MV IIlIICblnea with beam hnrdtztIng f1allell!ng filters of low atomlo nombet IIllIkIns vetj' penetrative narrow beamsnear theCBllll'al axil whereu the periphery of brol!d beams Ismuch 10fler. A maah more VDlfonn brow! beam pfOfilllat rI1 depths II obllllned willi lIOIIloed photon blllllUJ whllll> the bardeat pboton oompooent 18 at theperiphery of thebeam to oompemalci tor the ionget raylengtb. In betwlloo IlI'O spectrally compensating lillOl'll and the mosl common group using thick high atomic IIUmbor flitlit'. Doe to tIICl ciCIO relatloo between Jlen ond I\> it can be sbown lhat aIlonuatiDll dala am 'I8Il cloacly related to the ef'feotive llOppinl power ratio of photon beams, However, some authon have proposed the useof beam modifiers snc:h as clcc:troll film or special nmow blllll1 ool1lmlton for detennInatlon of beam attenuation . This should be avoided as far. possible as the beam to be IllCIIIQred will beoonsIdenbly Inf1uooc:ed bytbem and!hilithedosimetry more unc:ertaIn.
120 ON AXIS AND OFF AXIS BREMSSTRAHLUNG ENERGY SPECTRA CALCULATED BY EGS4 MONTE~ARLO CODE
SHI LIU. PEDROANDREO,ANDERS SATIlERBERGI,IRENA GUDOWSKA and ANDERSBRAHME Dept Medical Radiation Physics, Karolinska Institutet - University of Stockholm, S-I71 76 Stockholm, Sweden; I Dept Radiation Physics, University of Umea, S-901 85 Umea, Sweden
S. ZEFKILI, InstitutPaoli·GaJmeltes, Marseille, FRANCE G. MALA-TARA, K. KAPPAS, Universityof Palras, Patras, GREECE J .C . ROSENWALD,lnstftut Curie, Paris, FRANCE
Within the frame of our programme on realistic Monte Carlo calculations for dosimetry and treatment planning, the detailed simulation of the treatment head of radiotherapy accelerators has been focused on a MM50 Racetrack microtron . The project includes the improvement of bremsstrahlung target design and the effect of neutron production on the irradiation of patients with high-energy scanned beams. Most applications by other autho rs have so far used the EGS4 Monte Carlo system.; their implementation has been usually based on the coding of the speci fic geometry of each machine. Our project concentrates in using " public" and standard ized software tools for both geometry descr iption and simulation to minim ize manpowe r and economi cal requ irem ents. Accelerator head structures are described using the Combinatorial Geometry (CG) package where 3D "bodies" are combined using Boolean algebra; this enables an almost universal characterization that can be easily adapted to any accelerator treatment head. Graphical visualizatio n is accomplished with the code SABRINA, which processes both CG (and specific input s for the MCNP Monte Carlo system); SABRINA runs in almost every UNIX workstation. Simulations are performed with the ACCEPT code of the ITS 3.0 MC system , full y based on CG inputs and containing "state- of-the-art" brems strahlung cross·sections; it also allows a direct implementation of the purging magnet in the MMSO head. Our interest in neutron production will consider the utiliz ation of MCNP when a planned version containing the electron transport of ITS 3.0 becomes a reality. All the software is available in Europe through the NEA data bank . This presentation will describe the selected tools and actual status of the project. Support from K Van Riper (LANL) and R Kensek and J Halbleib (Sandia Labs) is greatly acknowledged.
For accurate 3D treatment planning new models of dose calculation are being developed which require the knowledge of the energy spectra of photons incident on the surface of the patients. In this study the EGS4 Monte·Carlo code system wrth the PRESTA electron transport algorithm was used in order to compute the photon energy spectra at on axis and off-axis points for a number of Iinacs manufactured by G.E. The different parts 01 the accelerator head were modeled by simple geometrical volumes and the photon beams were produced by simulating the bombarding of the target wrth monoenergetic electron beams assumed to have a spatial distribution. The analysis of the cak:IJlated spectra wrth and without flattening filter showed us the photon beam quality variation at off-axispoints. To verify the validity of the calculated spectra we introduced them as input to a dose spread arrays convolution program in order to calculate TMRas a functionof depth of the total and primary dose distribution in a water1ike fantom. The calculated depth dose distributions were compared with experimental data . The theoretica l and experimental resuns are consistent and allow us to consider that the photon energy spectra can be determined with acceptable accuracy using Monte Carlosimulations even with a simptrtied acce lerator head geometry.